To induce antigen-specific T cell activation and clonal expansion, two signals provided by antigen-presenting cells (APCs) must be delivered to the surface of resting T lymphocytes (Jenkins, M. and Schwartz, R. (1987) J. Exp. Med 165, 302-319; Mueller, D. L., et al. (1990) J. Immunol. 144, 3701-3709; Williams, I. R. and Unanue, E. R. (1990) J. Immunol. 145, 85-93). The first signal, which confers specificity to the immune response, is mediated via the T cell receptor (TCR) following recognition of foreign antigenic peptide presented in the context of the major histocompatibility complex (MHC). The second signal, termed costimulation, induces T cells to proliferate and become functional (Schwartz, R. H. (1990) Science 248, 1349-1356). Costimulation is neither antigen-specific, nor MHC restricted and is thought to be provided by one or more distinct cell surface molecules expressed by APCs (Jenkins, M. K., et al. (1988) J. Immunol. 140, 3324-3330; Linsley, P. S., et al. (1991) J. Exp. Med. 173, 721-730; Gimmi, C. D., et al., (1991) Proc. Natl. Acad. Sci. USA. 88, 6575-6579; Young, J. W., et al. (1992) J. Clin. Invest. 90, 229-237; Koulova, L., et al. (1991) J. Exp. Med. 173, 759-762; Reiser, H., et al. (1992) Proc. Natl. Acad. Sci. USA. 89, 271-275; van-Seventer, G. A., et al. (1990) J. Immunol. 144,4579-4586; LaSalle, J. M., et al., (1991) J. Immunol. 147, 774-80; Dustin, M. I., et al., (1989) J. Exp. Med. 169, 503; Armitage, R. J., et al. (1992) Nature 357, 80-82; Liu, Y., et al. (1992) J. Exp. Med. 175, 437-445). One costimulatory pathway involved in T cell activation involves the molecule CD28 on the surface of T cells. This molecule can receive a costimulatory signal delivered by a ligand on B cells or other APCs. Ligands for CD28 include members of the B7 family of B lymphocyte activation antigens such as B7-1 and/or B7-2 (Freedman. A. S. et al. (1987) J. Immunol. 137, 3260-3267; Freeman, G. J. et al. (1989) J. Immunol. 143, 2714-2722; Freeman, G. J. et al. (1991) J. Exp. Med. 174, 625-631; Freeman, G. J. et al (1993) Science 262, 909-911; Azuma, M. et al. (1993) Nature 366, 76-79; Freeman, G. J. et al. (1993) J. Exp. Med. 178, 2185-2192). B7-1 and B7-2 are also ligands for another molecule, CTLA4, present on the surface of activated T cells, although the role of CTLA4 in costimulation is unclear.
Delivery to a T cell of an antigen-specific signal with a costimulatory signal leads to T cell activation, which can include both T cell proliferation and cytokine secretion. In contrast, delivery to a T cell of an antigen-specific signal in the absence of a costimulatory signal is thought to induce a state of unresponsiveness or anergy in the T cell, thereby inducing antigen-specific tolerance in the T cell.
Interactions between T cells and B cells play a central role in immune responses. Induction of humoral immunity to thymus-dependent antigens requires xe2x80x9chelpxe2x80x9d provided by T helper (hereafter Th) cells. While some help provided to B lymphocytes is mediated by soluble molecules released by Th cells (for instance lymphokines such as IL-4 and IL-5), activation of B cells also requires a contact-dependent interaction between B cells and Th cells. Hirohata et al., J. Immunol., 140:3736-3744 (1988); Bartlett et al., J. Immunol., 143:1745-1754 (1989). This indicates that B cell activation involves an obligatory interaction between cell surface molecules on B cells and Th cells. The molecule(s) on the T cell therefore mediates contact-dependent helper effector functions of the T cell. A contact-dependent interaction between molecules on B cells and T cells is further supported by the observation that isolated plasma membranes of activated T cells can provide helper functions necessary for B cell activation. Brian, Proc. Natl. Acad Sci. USA, 85:564-568 (1988); Hodgkin et al., J. Immunol., 145:2025-2034 (1990); Noelle et al., J. Immunol., 146:1118-1124 (1991).
A molecule, CD40, has been identified on the surface of immature and mature B lymphocytes which, when crosslinked by antibodies, induces B cell proliferation. Valle et al., Eur. J. Immunol., 19:1463-1467 (1989); Gordon et al., J. Immunol., 140:1425-1430 (1988); Gruber et al., J. Immunol., 142: 4144-4152 (1989). CD40 has been molecularly cloned and characterized. Stamenkovic et al., EMBO J., 8:1403-1410 (1989). A ligand for CD40, gp39 (also called CD40 ligand or CD40L) has also been molecularly cloned and characterized. Armitage et al., Nature, 357:80-82 (1992); Lederman et al., J. Exp. Med., 175:1091-1101 (1992); Hollenbaugh et al, EMBO J., 11:4313-4319 (1992). The gp39 protein is expressed on activated, but not resting, CD4+ Th cells. Spriggs et al., J. Exp. Med., 176:1543-1550 (1992); Lane et al., Eur. J. Immunol., 22:2573-2578 (1992); Roy et al., J. Immunol., 151:1-14 (1993). Cells tansfected with the gp39 gene and expressing the gp39 protein on their surface can trigger B cell proliferation and, together with other stimulatory signals, can induce antibody production. Armitage et al., Nature, 357:80-82 (1992); Hollenbaugh et al., EMBO J., 11:4313-4319 (1992).
Cell-surface molecules which mediate contact-dependent helper effector functions of T cells are important for inducing immune responses which require T cell help. For example, the interaction of gp39 on T cells with CD40 on B cells plays a central role in activating B cell responses to an antigen. The current invention is based, at least in part, on the discovery that cell-surface molecules which mediate contact-dependent helper effector functions of T cells also play a critical role in the response of T cells to alloantigens. In particular, it has been discovered that, under appropriate conditions, interference with an interaction of gp39 with a ligand on an allogeneic cell which is presenting alloantigens to the T cell can induce tolerance in the T cell. Preferably, the allogeneic cell which presents alloantigens to the T cell requires an interaction between a gp39 ligand on the cell and gp39 on the T cell to be able to provide signals necessary for activation of the T cell. Inhibiting the interaction of the gp39 ligand on the allogeneic cell with gp39 on the T cell prevents T cell activation and rather induces alloantigen-specific T cell tolerance. Induction of T cell tolerance to alloantigens as described herein can be used as a preparative regimen for tissue or organ transplantation.
Accordingly, the methods of the invention are particularly useful for inducing T cell tolerance to a donor tissue or organ in a recipient of the tissue or organ The methods involve administering to a transplant recipient: 1) an allogeneic or xenogeneic cell which expresses at least one donor antigen and which has a ligand on a cell surface which interacts with a receptor on the surface of a recipient T cell which mediates contact-dependent helper effector functions; and 2) an antagonist of the molecule on the surface of the recipient T cell which mediates contact-dependent helper effector functions. The antagonist inhibits an interaction between the molecule on the T cell and it""s ligand on the allogeneic or xenogeneic cell.
In a preferred embodiment, the receptor on the surface of a recipient T cell which mediates contact-dependent helper effector functions is gp39. In this embodiment, the antagonist is a molecule which inhibits the interaction of gp39 on a T cell with a gp39 ligand on an allogeneic or xenogeneic cell. A particularly preferred gp39 antagonist is an anti-gp39 antibody. In another embodiment, the gp39 antagonist is a soluble form of a gp39 ligand, for example soluble CD40. The allogeneic or xenogeneic cell which is administered to the recipient is preferably a lymphoid cell, for example a B cell. Alternatively, the allogeneic or xenogeneic cell is a small resting B cell. The allogeneic or xenogeneic cell and the antagonist (e.g., anti-gp39 antibody) are typically administered to a recipient subject prior to transplantation of the tissue or organ into the subject For example, lymphoid cells (e.g., B cells) from the donor of the tissue or organ are administered to the recipient, together with the antagonist, prior to transplantation of the tissue or organ into the recipient.
The methods of the current invention can be used, for example, to induce T cell tolerance to transplanted tissue or organs such as liver, kidney, heart, lung, skin, muscle, neuronal tissue, stomach and intestines. In one embodiment, the transplanted tissue comprises pancreatic islets. Accordingly, the invention provides a method for treating diabetes comprising administering to a subject in need of treatment: 1) allogeneic or xenogeneic cells which express donor antigens; 2) an antagonist of a receptor on the surface of recipient T cells which mediates contact-dependent helper effector functions, such as a gp39 antagonist (e.g., an anti-gp39 antibody); and 3) donor pancreatic islets.